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// SPDX-License-Identifier: GPL-2.0
/*
* Test the 'D' (register disabled) flag of binfmt_misc. An entry
* registered with it exists but cannot be matched until userspace enables
* it, which splits a registration into create and activate.
*
* Needs root for the registration; no bpf toolchain involved.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include "binfmt_misc_common.h"
#include "kselftest_harness.h"
#define MAGIC "#DISABLED-SELFTEST#"
#define TARGET_PATH "/tmp/binfmt_disabled_target"
#define INTERP_PATH "/tmp/binfmt_disabled_interp.sh"
#define ENTRY "test_disabled"
#define RULE(flags) ":" ENTRY ":M:0:" MAGIC "::" INTERP_PATH ":" flags
/* The interpreter exits with a code the harness can recognise. */
#define EXIT_INTERP 7
/* The target only has to carry the magic; it is never actually loaded. */
static int create_target(void)
{
char buf[128] = MAGIC "\n";
int fd;
unlink(TARGET_PATH);
fd = open(TARGET_PATH, O_WRONLY | O_CREAT | O_EXCL, 0755);
if (fd < 0)
return -1;
if (write(fd, buf, sizeof(buf)) != (ssize_t)sizeof(buf)) {
close(fd);
return -1;
}
close(fd);
return 0;
}
static int create_interp(void)
{
char buf[64];
int fd;
unlink(INTERP_PATH);
fd = open(INTERP_PATH, O_WRONLY | O_CREAT | O_EXCL, 0755);
if (fd < 0)
return -1;
snprintf(buf, sizeof(buf), "#!/bin/sh\nexit %d\n", EXIT_INTERP);
if (write(fd, buf, strlen(buf)) != (ssize_t)strlen(buf)) {
close(fd);
return -1;
}
return close(fd);
}
FIXTURE(disabled) {
};
FIXTURE_SETUP(disabled)
{
if (getuid() != 0)
SKIP(return, "test must be run as root");
if (!binfmt_misc_available())
SKIP(return, "no binfmt_misc");
/* Skip the whole suite on a kernel that does not know 'D'. */
if (!binfmt_flag_supported('D')) {
ASSERT_EQ(errno, EINVAL);
SKIP(return, "kernel without the 'D' flag");
}
ASSERT_EQ(create_interp(), 0);
ASSERT_EQ(create_target(), 0);
}
FIXTURE_TEARDOWN(disabled)
{
unregister(ENTRY);
unlink(TARGET_PATH);
unlink(INTERP_PATH);
}
/* The entry exists but does not dispatch until it is enabled. */
TEST_F(disabled, inert_until_enabled)
{
ASSERT_EQ(write_reg(RULE("D")), 0);
EXPECT_TRUE(entry_shows(ENTRY, "disabled"));
/* Nothing matches it, so no binary format claims the target. */
EXPECT_EQ(run_payload(TARGET_PATH), RUN_ENOEXEC);
ASSERT_EQ(entry_command(ENTRY, "1\n"), 0);
EXPECT_TRUE(entry_shows(ENTRY, "enabled"));
EXPECT_EQ(run_payload(TARGET_PATH), EXIT_INTERP);
}
/* Without 'D' an entry is matchable the moment it is registered. */
TEST_F(disabled, enabled_without_the_flag)
{
ASSERT_EQ(write_reg(RULE("")), 0);
EXPECT_TRUE(entry_shows(ENTRY, "enabled"));
EXPECT_EQ(run_payload(TARGET_PATH), EXIT_INTERP);
}
/* 'D' is spent on the registration: the entry does not report it back. */
TEST_F(disabled, flag_not_reported)
{
ASSERT_EQ(write_reg(RULE("D")), 0);
EXPECT_FALSE(entry_shows(ENTRY, "flags: D"));
EXPECT_TRUE(entry_shows(ENTRY, "flags: "));
}
/* A disabled entry can be disabled and enabled like any other. */
TEST_F(disabled, toggles_like_any_entry)
{
ASSERT_EQ(write_reg(RULE("D")), 0);
ASSERT_EQ(entry_command(ENTRY, "1\n"), 0);
ASSERT_EQ(run_payload(TARGET_PATH), EXIT_INTERP);
ASSERT_EQ(entry_command(ENTRY, "0\n"), 0);
EXPECT_EQ(run_payload(TARGET_PATH), RUN_ENOEXEC);
ASSERT_EQ(entry_command(ENTRY, "1\n"), 0);
EXPECT_EQ(run_payload(TARGET_PATH), EXIT_INTERP);
}
/* 'D' composes with the invocation flags a static entry can carry. */
TEST_F(disabled, composes_with_invocation_flags)
{
ASSERT_EQ(write_reg(RULE("PD")), 0);
EXPECT_TRUE(entry_shows(ENTRY, "disabled"));
EXPECT_TRUE(entry_shows(ENTRY, "flags: P"));
}
/* '-1' to the status file sweeps a staged entry with everything else. */
TEST_F(disabled, removed_by_remove_all)
{
int fd;
ASSERT_EQ(write_reg(RULE("D")), 0);
EXPECT_TRUE(entry_shows(ENTRY, "disabled"));
fd = open(BINFMT_DIR "/status", O_WRONLY | O_CLOEXEC);
ASSERT_GE(fd, 0);
ASSERT_EQ(write(fd, "-1", 2), 2);
close(fd);
EXPECT_NE(access(BINFMT_DIR "/" ENTRY, F_OK), 0);
}
/* A file handle held across a removal cannot resurrect the entry. */
TEST_F(disabled, no_resurrection_after_remove)
{
int fd;
ASSERT_EQ(write_reg(RULE("D")), 0);
fd = open(BINFMT_DIR "/" ENTRY, O_WRONLY | O_CLOEXEC);
ASSERT_GE(fd, 0);
ASSERT_EQ(write(fd, "-1", 2), 2);
EXPECT_NE(access(BINFMT_DIR "/" ENTRY, F_OK), 0);
/* Accepted like any toggle of a removed entry, but publishes nothing. */
EXPECT_EQ(write(fd, "1", 1), 1);
EXPECT_EQ(run_payload(TARGET_PATH), RUN_ENOEXEC);
close(fd);
}
TEST_HARNESS_MAIN
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